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Observe the picture given… (Class 12 Biology 2024, Q18)

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BiologyCBSE Class 12 · Board exam 2024, set 57/1/1 · 2 marks · Very short answer

CBSE Class 12 Biology 2024: question 18

Set in the CBSE Class 12 board exam of 2024, paper 57/1/1, section B, question 18, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q18 · 2 marks · Very short answerCompetency-basedEvolution

Observe the picture given below. Name the naturalist and write the explanation given by him that evolution of life forms had occurred on the basis of this example.

Figure in the paper: Series of giraffes of increasing neck length from left to right, the shortest one grazing on the ground and progressively taller giraffes reaching for leaves on progressively taller trees. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 57/1/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Which early naturalist explained evolution through giraffe necks?

Hint 2

His theory rests on two ideas: how much an organ is used, and whether acquired traits are passed on.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. The naturalist is Jean-Baptiste Lamarck.

    ½ mark

  2. Lamarck held that evolution of life forms is driven by the use and disuse of organs: organs that are used more get strengthened or enlarged, and those not used weaken.

    ½ mark

  3. In his example, the ancestors of giraffes stretched their necks repeatedly to reach and forage leaves on tall trees. As a result, their necks gradually elongated within their lifetime.

    ½ mark

  4. This acquired character (a longer neck) was passed on to the next generation. Over many generations, the inheritance of acquired characters produced the present-day long-necked giraffes.

    ½ mark

Answer: Lamarck; use and disuse of organs, with acquired characters (elongated neck) inherited over generations

Where the marks are

  • Names Lamarck (½ mark)
  • Use and disuse of organs as the driving force (½ mark)
  • Giraffes elongated their necks while foraging on tall trees (½ mark)
  • Acquired long neck inherited by succeeding generations (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Evolution, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 57/1/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.